A trench gate structure is used, for example, in power MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors). The trench gate structure includes a gate oxide film formed on an inner wall surface of a trench formed on a semiconductor substrate and a polysilicon gate embedded in the trench so as to be contiguous to the gate oxide film. The semiconductor substrate has a source region, a channel region, and a drain region formed in order from the surface of a semiconductor device in the thickness direction of the semiconductor substrate. The trench penetrates the source region and the channel region, and reaches the drain region. Therefore, the polysilicon gate faces the source region, the channel region, and the drain region through the gate oxide film. A MOSFET is arranged in this way.
A connection of a gate electrode to the polysilicon gate is performed in an area outside the trench. Therefore, the polysilicon gate has a stranded portion that has been drawn out from the inside of the trench and that has been stranded on regions on the semiconductor substrate outside the trench. The gate electrode is connected to the stranded portion.